class_docstr: Class used for managing plot data
    - allows data sharing between multiple graphics items (curve, scatter, graph..)
    - each item may define the columns it needs
    - column groupings ('pos' or x, y, z)
    - efficiently appendable 
    - log, fft transformations
    - color mode conversion (float/byte/qcolor)
    - pen/brush conversion
    - per-field cached masking
      - allows multiple masking fields (different graphics need to mask on different criteria) 
      - removal of nan/inf values
    - option for single value shared by entire column
    - cached downsampling
    - cached min / max / hasnan / isuniform
code: def __init__(self):
      self.fields = {}
  
      self.maxVals = {}  ## cache for max/min
      self.minVals = {}
  
file_path: pyqtgraph/pyqtgraph/PlotData.py
imports: import numpy
label_desc: Use image node_id 1 to create a new PlotData object from inherited base classes: object with example: obj = PlotData()